This invention relates to dispensing apparatus for multi-component foam systems and more particularly, it concerns a solvent cleaning provision for such apparatus.
Foam dispensing guns of the type disclosed in U.S. Pat. Nos. 3,784,110; 4,311,254 and 4,399,930 were developed principally for use with prepackaged foam kits including the two pressurized containers of foam forming chemicals or resins, a dispensing gun and other supplies incidental to dispensing of the supplied resins as foam, such as hoses for attaching the gun to the containers, petroleum jelly for assuring sealed connections of couplings, solvent for cleaning the resins from the gun and a plurality of nozzles adapted for easy replacement in the gun. The resins, commonly referred to as the "A resin" and the "B resin" are supplied separately in the two containers and are typically polymeric isocyanate and polyol amines, respectively. The design of the overall system is such that the separately supplied resins are kept from contact with each other until they are mixed in and discharged from the gun nozzle. The mixture of resins quickly sets up as a rigid foam product which is substantially insoluble and thus extremely difficult, if not impossible, to remove from surfaces with which it comes in contact. Also, because of these characteristics, any substantial interruption in operation of the gun is likely to cause the mixed resins to set up in the nozzle itself and thus prevent further foam dispensing operation. It is for this reason that the nozzles of the gun are replaceable and that each prepackaged kit or system is provided with an adequate supply of the replaceable nozzles.
When the dispensing gun, connected by hoses to the pressurized containers of the two resins, is to be left unattended for an extended period of time such as a lunch break or overnight, recommended procedure involves removing the used nozzle and cleansing the gun of any residual resin using the solvent supplied with the pre-packaged kit. In this respect, the B resin or polyol amine is relatively inert and will remain as a liquid even when exposed to air for a substantial period of time. The A resin or polymeric isocyanate, on the other hand, will solidify upon exposure to air and in time will present a clogging problem or otherwise cause malfunction of relatively movable parts such as valve components with which the A resin comes in contact. The solvent supplied with each kit, therefore, is principally intended to dissolve the unmixed A resin and effectively remove it from any portion of the gun with which it comes it contact after passing the gun valve which isolates from the atmosphere the A resin remaining in passageways extending from the tank up to the valve. However, it is difficult in practice to assure circulation of the solvent into gun parts and other internal surfaces located downstream from the A resin valve. The result of this difficulty, in turn, is often clogging of the A resin passageway to a point where the gun is no longer useful for dispensing all of the resin supplied with each kit.
The replaceable nozzle foam dispensing guns heretofore developed have been highly effective with prepackaged resin kits capable of supplying up to 50 cu. ft. or more of the dispensed foam product. Moreover, the dispensing guns presently in use are highly effective in terms of meeting the economic constraints of temporary use, that is, disposal after resin supplied with each package or kit is dispensed. There is a need however for alleviating the problem of clogged ports and gun valving as a result of the A resin hardening upon exposure to the atmosphere.